Translucent high-temperature powder coatings

ABSTRACT

Coating powders are provided which provide high-temperature, translucent coatings useful for light-emitting devices such as incandescent bulbs. The coating powders comprise a binder, at least 90 wt % up to 100 wt % of which is a silicone resin. The coating powders are filled with between about 10 and about 50 phr of fillers selected from the group consisting of needle-like calcium metasilicate, mica, rod-like glass particles, and mixtures thereof, the fillers having aspect ratios between about 8 and about 40.

The present application is a Division of U.S. Application Ser. No.09/289,536, filed on Apr. 9, 1999, now U.S. Pat. No. 6,248,824 B1.

The present invention is directed to coating powders which producetranslucent coatings particularly suitable for coating light-emittingdevices, such as incandescent light bulbs.

BACKGROUND OF THE INVENTION

High-temperature, light-emitting devices, such as incandescent lightbulbs are conventionally coated for translucency with liquid coatingscomprising silicone resins in organic solvents. There is a general needto replace such hazardous and polluting coatings with non-hazardous andnon-polluting powder coatings.

Powder coating compositions which yield transparent or translucentcoatings are well known in the art. Typical organic binder materials forsuch coatings are epoxy, polyester, and acrylic resins. Unfortunately,coatings based on these organic binder systems darken and decompose uponprolonged exposure at typical incandescent operating temperatures of 300to 700° F. (149 to 371° C.) and thus are not useful for light-emittingdevices. Coatings containing blends of silicones and significant levelsof organic binders, such as those disclosed in U.S. Pat. Nos. 5,684,066to Eklund and 4,877,837 to Reisling also discolor and similarly are notuseful for light-emitting devices.

Coating powders based totally on silicone resins or substantiallyentirely on silicone resins are known. For example, Daly et al. in U.S.Pat. No. 5,422,396 disclose in a “comparative example” a 100% siliconeresin based on Dow Corning 6-2230 silicone resin. The “comparativeexample” formulation in Daly et al. contained 80 phr (parts per hundredresin by weight) mica. Although silicone-based powder coatings having aslow as 40 phr mica or other reinforcing filler have been described,higher levels such as 60 phr and upward are generally used inhigh-temperature coatings. Below about 60 phr filler levels, coatingstend to be insufficiently reinforced for high-temperature use as suchcoatings tend to crack and peel at high temperatures.

Silicone coatings containing 60 to 80 phr and upward filler, such asmica and/or wollastonite (calcium metasilicate) are resistant tocracking and peeling at high temperatures. However, such fillerscontribute to opacity and yellowing of the coatings, and filler levelsof 60 phr give coatings which are too rough and too opaque to begenerally useful for light-emitting devices.

It is a general object of the invention to provide coating powders forproducing translucent coatings on high-temperature substrates, such aslight-emitting devices including incandescent bulbs.

SUMMARY OF THE INVENTION

In accordance with the invention there are provided coating powderswhich provide high-temperature, translucent coatings useful forlight-emitting devices such as incandescent bulbs. The coating powderscomprise a binder, at least 90 wt %, preferably at least 95 wt % up to100 wt % of which is a silicone resin. The coating powders are filledwith between about 10 and about 50 phr, preferably between about 20 andabout 40 phr, most preferably between about 25 and about 35 phr offillers selected from the group consisting of needle-like calciummetasilicate, mica, rod-like glass particles, and mixtures thereof, thefillers having aspect ratios between about 8 and about 40, preferablybetween about 10 and about 25. The high aspect ratio of the fillersprovide high-temperature reinforcement to the coatings at use levelssufficiently low to provide sufficient light transmittance for use withlight-emitting devices.

The invention provides light-emitting devices, such as glassincandescent bulbs, having coatings derived from silicone-based coatingpowders, such coatings providing light transmittance at 1 milthicknesses of at least 50%, preferably at least 80%.

The invention further provides coating powders having binders which areat least 90 wt % silicone, preferably at least 95 wt % silicone andwhich contain between about 0.05 and about 3 phr of zincdialkylcarboxylate wherein the alkylcarboxylate ligands contain between6 and 20 carbon atoms. Preferably, the alkylcarboxylate ions arebranched at the carbon alpha to the carboxylate group. Such a catalystis zinc neodecanoate.

DETAILED DESCRIPTION OF CERTAIN PREFERRED EMBODIMENTS

Herein, unless otherwise noted, percentages are by weight. The resins inthe coating powders are calculated at 100%, and other components areexpressed as percentages relative to 100% resin.

Heretofore, fillers such as mica and calcium metasilicate used forhigh-temperature, silicone-based coatings had relatively low aspectratios, e.g., 5:1 and 3:1 being typical. The aspect ratio of needle-likewollastonite and rod-like glass particles are the ratio of length towidth or diameter. The aspect ratio of platelet-like mica particles isthe ratio of the diameter to the thickness. In respect to aspect ratios,it is understood that these are average aspect ratios of the individualparticles. Surprisingly, it is found that by using fillers with higheraspect ratios, enhanced high-temperature reinforcement if provided atlower filler use levels. High aspect ratio needle-like calciummetasilicate, rod-like glass particles, and mica, at use levels in the10 to 50 phr, provide sufficient translucency to be used for coatinglight-emitting devices, particularly incandescent bulbs.

Coatings on incandescent bulbs formed from the coating powders of thepresent invention are typically about 1 mil (25 microns) thick, but mayrange from 0.5 to 2 mils thick. As a standard, therefore, at 1 milthickness, the coatings formed from the coating powders of the presentinvention should provide at least 50% light transmittance, preferably atleast 80% light transmittance, although for the thinner coatings it maybe possible to,use more opaque coatings. The fillers allow sufficientlight transmittance but do impart some translucency. For un-coloredcoatings, the coating powders of the present invention should provide,at least 80% light transmittance at 1 mil thickness. Colored coatingscontaining high-temperature stable pigments will transmit less light,depending upon the type and amount of pigment.

Silicone resins self cure by the condensation of siloxyl (SiOH) endgroups of silicone resins by the reaction:

Accordingly, the binder resin may be 100 wt % silicone withoutadditional cross-linking agent. Silicone/glycidyl methacrylate coatingsare described in Reisling (U.S. Pat. No. 4,887,837) and Eklund (U.S.Pat. No. 5,684,066) and silicone/acid-functional acrylic/triglycidylisocyanurate compositions are described in Daly et al. (U.S. Pat. No.5,422,396). The teachings of each of these patents is incorporatedherein by reference. Organic resins in addition to the silicone resinsare permissible in the coating powders of the present invention,providing such organic resins do not comprise more than 10 wt % of thebinder system preferably no more than about 5 wt % of the binder systemso as to minimize yellowing of the coating over time withhigh-temperature exposure. Such non-silicone resins includecross-linking agents such as those described above in U.S. Pat. Nos.5,684,066 and 5,422,396 and resins added for purposes such as flowcontrol, gas release, etc.

Preferred silicone resins have organic substitutents selected from thegroup consisting of phenyl, methyl, C₂ through C₆ alkyl and mixturesthereof. Preferred silicone resins have viscosities of between about 500and about 10,000 cps at 150° C., most preferably 2000 to 5000 cps. Thepreferred silicone resins have condenseable hydroxyl contents of betweenabout 2 and about 4.5 wt %, preferably from about 2 to about 3 wt. %.Preferred silicone resins have glass transition temperatures (Tg) ofabout 55° C. or above, preferably about 60° C. or above. Preferredsilicone resins contain about 0.2% or less of organic solvents, morepreferably about 0.1% or less.

Coating powders in accordance with the present invention are formed in aconventional manner. The components of the coating powder are batchedand shaken, e.g., for 5 minutes, to blend well. The materials are thenextruded, e.g., at 100° C. (230° F.) in a Buss single screw extruder,allowed to cool, chipped, ground and screened to obtain a powder ofappropriate size. Average particle size is typically 20-80 microns.Scalping at 100 mesh is typical to remove coarse particles. There istypically about 10% by weight of particles below 10 microns. The amountof material retained on a 325 mesh is typically between about 30 to 50wt. %. The powder is then applied in a conventional manner, e.g.,electrostatically, to a substrate. The substrate is heated at the timeof application and/or subsequently so that the coating particles form acontinuous film, and, especially in the case of isocyanate-curedsilicone resin adducts, effect the cure.

The invention will now be discussed in greater detail by way of specificexamples.

RAW MATERIALS

Morkote S-101 A hydroxy-functional phenylmethylpolysiloxane resinmanufactured by Morton International, Inc. This resin has a reactivehydroxyl content of approximately 2.3%, a viscosity at 150° C. of 2700cP and a T_(g) of 64° C.

Silres 601 A hydroxy-functional phenylpolysiloxane resin sold by WackerSilicones.

GMA 300 An epoxy-functional acrylic sold by Estron Chemical.

Zinc Acetvlacetonate A hydrated zinc enolate sold by GCA Chemical.

Zinc Neodecanoate A zinc alkylcarboxylate sold by OMG Americas.

Zinc Stearate Sold by Smith Chemical and Color.

Nyad 325 A 325 mesh wollastonite sold by Eastech Chemicals.

Orleans 325 A 325 mesh wollastonite sold by Ressources Orleans Inc.

Orleans 1 A 100 mesh wollastonite sold by Ressources Orleans Inc.

737 BC A chopped glass fiber sold by Owens Corning.

C-3000 Mica A muscovite mica sold by Eastech Chemicals.

Troy 486-CFL An acrylic flow aid sold by Troy Chemical Corp.

COMPARATIVE EXAMPLE 1

This comparative example illustrates a basic silicone binder systemcomposed of heat-curable silicone resins with no curing agent or filler.The coating is smooth and nearly transparent, but is not useful as acoating because it is easily cracked by mechanical damage or heatexposure.

The components listed under Comparative Example 1 in Table 1 below werecompounded, chilled, chipped, ground and sieved through a 200 meshscreen in the usual manner to prepare a coating powder. This powder waselectrostatically sprayed onto the following substrates: 0.032inch-thick mild steel panels “Q” panels, 0.011 inch thick black andwhite “opacity” panels, and 0.039 inch thick soft glass slides. Thecoating was cured in a 450° F. oven for 15 minutes. Properties andperformance were measured on coatings which were 0.8 to 1.2 mils thick.Mechanical properties were measured on “Q” panels, color was measured onblack and white “opacity” panels, and crack resistance over glass wasmeasured on glass slides. Results are recorded in Table 2 below.

COMPARATIVE EXAMPLE 2

This example illustrates the performance of a coating which is notuseful as a translucent, high temperature coating because it contains 10parts of an acrylic curing agent. When exposed to 500° F. for 16 hours,the coating darkened (ΔL=−3.6), and cracked. Exposure at 600° F. gavemore darkening (ΔL=−6.8) and cracking.

The components listed under Comparative Example 2 in Table 1 werecompounded, chilled, chipped, ground and sieved through a 200 meshscreen in the usual manner to prepare a coating powder. This powder waselectrostatically sprayed onto the various substrates, cured in a 450°F. oven for 15 minutes and tested as in Comparative Example 1. Resultsare recorded in Table 2.

COMPARATIVE EXAMPLE 3

This example illustrates the performance of a coating which contains 60parts of reinforcing filler, a filler quantity which is beyond thatgenerally useful for translucent coatings. The high filler levelproduced a color difference from the unfilled control of ΔE=6.5. Thecoating was severely textured, with a 60° gloss of 19).

The components listed under Comparative Example 3 in Table 1 werecompounded, chilled, chipped, ground and sieved through a 200 meshscreen in the usual manner to prepare a coating powder. This powder waselectrostatically sprayed onto the various substrates, cured in a 450°F. oven for 15 minutes and tested as in Comparative Example 1. Resultsare recorded in Table 2.

COMPARATIVE EXAMPLE 4

This example discloses the performance of a coating which contains noreinforcing filler, but which is cured with zinc neodecanoate. It showsthe smoothness and lack of bubbles and pinholes typical of zincneodecanoate coatings, as well as the susceptibility to cracking on heatexposure of coatings containing no reinforcing filler. It was used asthe color standard against which other coatings were compared. Incontrast to the uncatalyzed coating, when tested for 16 hours at 500°F., cracking was not observed. When tested 16 hours at 600° F., however,large continuous cracks formed.

The components listed under Comparative Example 4 in Table 1 werecompounded, chilled, chipped, ground and sieved through a 200 meshscreen in the usual manner to prepare a coating powder. This powder waselectrostatically sprayed onto the various substrates, cured in a 450°F. oven for 15 minutes and tested as in Comparative Example 1. Resultsare recorded in Table 2.

EXAMPLE 1

This example discloses the performance of a coating which contains 10parts of reinforcing filler. As expected, the presence of the micafiller added color to the coating, a total color difference from theunfilled coating (ΔE) of 2.8. The coating became more textured, asevidenced by a reduction of the 60° gloss from 104 to 86. No crackingwas observed at 500° F. Cracks from 600° F. testing shrank to typicallengths of 0.1 to 0.3 mm and became discontinuous.

The components listed under Example 1 in Table 1 were compounded,chilled, chipped, ground and sieved through a 200 mesh screen in theusual manner to prepare a coating powder. This powder waselectrostatically sprayed onto the various substrates, cured in a 450°F. oven for 15 minutes and tested as in Comparative Example 1. Resultsare recorded in Table 2.

EXAMPLE 2

This example discloses the performance of a coating which contains 25parts of reinforcing filler. As expected, the presence of the micafiller added color to the coating, ΔE=4.3. The coating became moretextured, as evidenced by a reduction of the 60° gloss to 68. Cracksfrom 600° testing shrank further to typical lengths of 0.02 to 0.1 mm.

The components listed under Example 2 in Table 1 were compounded,chilled, chipped, ground and sieved through a 200 mesh screen in theusual manner to prepare a coating powder. This powder waselectrostatically sprayed onto the various substrates, cured in a 450°F. oven for 15 minutes and tested as in Comparative Example 1. Resultsare recorded in Table 2.

EXAMPLE 3

This example discloses the performance of a coating which contains 40parts of reinforcing filler. The additional mica added color to thecoating, ΔE=7.1. The coating became more textured, as evidenced by areduction of the 60° gloss to 57. Cracks disappeared from the 600° testspecimens entirely.

The components listed under Example 3 in Table 1 were compounded,chilled, chipped, ground and sieved through a 200 mesh screen in theusual manner to prepare a coating powder. This powder waselectrostatically sprayed onto the various substrates, cured in a 450°F. oven for 15 minutes and tested as in Comparative Example 1. Resultsare recorded in Table 2.

COMPARATIVE EXAMPLE 5

This example discloses the performance of a coating which contains 25parts of a wollastonite reinforcing filler having a typical aspect ratioof 5 to 1. This filler caused a minimal color change from the unfilledsystem of ΔE=1.4. Cracks after 600° F. testing were discontinuous butrelatively large at lengths of 1-10 mm.

The components listed under Comparative Example 5 in Table 1 werecompounded, chilled, chipped, ground and sieved through a 200 meshscreen in the usual manner to prepare a coating powder. This powder waselectrostatically sprayed onto the various substrates, cured in a 450°F. oven for 15 minutes and tested as in Comparative Example 1. Resultsare recorded in Table 2.

EXAMPLE 5

This example discloses the performance of a coating which contains 25parts of a wollastonite reinforcing filler having a typical aspect ratioof 10 to 1. This filler caused a minimal color change from the unfilledsystem of ΔE=0.6. Crack; after 600° F. testing were very small and few.

The components listed under Example 5 in Table 1 were compounded,chilled, chipped, ground and sieved through a 200 mesh screen in theusual manner to prepare a coating powder. This powder waselectrostatically sprayed onto the various substrates, cured in a 450°F. oven for 15 minutes and tested as in Comparative Example 1. Resultsare recorded in Table 2.

EXAMPLE 6

This example discloses the performance of a coating which contains 25parts of a wollastonite reinforcing filler having an aspect ratio of 20to 1. This filler caused a minimal color change from the unfilled systemof ΔE=1.4. Cracks after 600° F. testing were small and discontinuous.

The components listed under Example 6 in Table 1 were compounded,chilled, chipped, ground and sieved through a 200 mesh screen in theusual manner to prepare a coating powder. This powder waselectrostatically sprayed onto the various substrates, cured in a 450°F. oven for 15 minutes and tested as in Comparative Example 1. Resultsare recorded in Table 2.

EXAMPLE 7

This example discloses the performance of a coating which contains 10parts of a wollastonite reinforcing filler having an aspect ratio of 20to 1. This filler caused a minimal color change from the unfilled systemof ΔE=0.9. Cracks after 600° F. testing were of moderate size anddiscontinuous.

The components listed under Example 7 in Table 1 were compounded,chilled, chipped, ground and sieved through a 200 mesh screen in theusual manner to prepare a coating powder. This powder waselectrostatically sprayed onto the various substrates, cured in a 450°F. oven for 15 minutes and tested as in Comparative Example 1. Resultsare recorded in Table 2.

EXAMPLE 8

This example discloses the performance of a coating which contains 25parts of a glass fiber reinforcing filler having an aspect ratio of 10to 1. This filler caused a minimal color change from the unfilled systemof ΔE=0.6. Cracks after 600° F. testing were large and numerous.Resistance to cracking was only marginally increased with thisreinforcing filler at this loading.

The components listed under Example 8 in Table 1 were compounded,chilled, chipped, ground and sieved through a 200 mesh screen in theusual manner to prepare a coating powder. This powder waselectrostatically sprayed onto the various substrates, cured in a 450°F. oven for 15 minutes and tested as in Comparative Example 1. Resultsare recorded in Table 2.

TABLE 1 Compositions¹ in Parts C. C. C. C. C. Ex. Component Ex. 1 Ex. 2³Ex. 3 Ex. 4 Ex.1 Ex. 2 Ex. 3 Ex. 5 Ex. 5 Ex. 6 Ex. 7 8 Morkote S-101² 7565 75 75 75 75 75 75 75 75 75 75 Silres 601² 25 25 25 25 25 25 25 25 2525 25 25 GMA-300² — 10 — — — — — — — — — — Zinc — — 0.5   0.5   0.5  0.5   0.5   0.5   0.5   0.5   0.5   0.5   neodecanoate² Nyad 325 — — — —— — — 25 — — — — Orleans 325 — — — — — — — — 25 — — — WollastoniteOrleans 1 — — — — — — — — — 25 10 — Wollastonite C-3000 Mica — 40 60 —10 25 40 — — — — — 737 BC Glass — — — — — — — — — — — 25 ¹Each coatingalso contained Troy 486-CFL², 2.0 phr; Benzoin, 0.8² phr. ²Bindercomponents ³Comparative Example 2 has a binder silicone level of 87%.All other compositions contain about 3 wt % non-silicone resins as flowads and thus had binder silicone levels of 97%.

TABLE 2 Performance C. Ex. C. Ex. C. Ex. C. Ex. C. Ex. Property 1 2 3 4Ex. 1 Ex. 2 Ex. 3 5 Ex. 5 Ex. 6 Ex. 7 Ex. 8 Gel Time (sec)   300+ 175231 240 265  273  243  147  137  166  184 279  Impact Resistance (in-lb)<20 160 160  20 40 100  160  20 20 20 <20 20 Pencil Hardness B 2H 2H H HH H F F F F F 60° Gloss (% Reflection) 114  27  19 104 86 68 57 64 67 69 85 81 Color Change (Compared lighter    5.5    6.5 —   2.8   4.3   7.1  1.4   0.6   1.4    0.9   0.6 to Ex. 1; white, ΔE)¹ 16 h, 500° F. HeatAge Crack Quantity 1-10  1-10 none none none none none none none nonenone none (per square mm)² Crack Length (mm) 1-5  .02-1.0 — — — — — — —— — — Darkening (ΔL)³ —   −3.6 — — — —   0.2 — — — — — 16 h, 600° F.Heat Age Crack Quantity 1-10  60 none  2 30 60 none 20  5 25  15 20 (persquare mm)² Crack Length (mm) 1-10 .02-.1  none 1-10 .1-.3 .02-.1 none1-10 .02-.1 .2-.5 .2-1.5 0.4-1.5 Darkening (ΔL)³ —   −6.8 — — — —   −2.3— — — — — Notes: ¹Measured on the CIELAB scale taking red-green,blue-yellow and black-white axis into account. ²Cracks were evaluatedusing a light microscope at 50X. ³Measured on the CIELAB scale whereblack is 0 and white is 100. The unit ΔL indicates the difference indarkness between the as-cured coating on a glass slide and a tested(heat-aged) slide.

EXAMPLE 9

This example discloses the performance of a coating which contains apreferred level of a reinforcing filler, but contains no curing agent.More and larger cracks were formed than were observed in coatings withcure catalyst in addition to filler, but fewer cracks were observed thanin un-reinforced systems.

The components listed under Example 9 in Table 3 were compounded,chilled, chipped, ground and sieved through a 200 mesh screen in theusual manner to prepare a coating powder. This powder waselectrostatically sprayed onto the various substrates, cured in a 450°F. oven for 15 minutes and tested as in Comparative Example 1. Resultsare recorded in Table 4.

EXAMPLE 10

This example discloses the performance of a coating which contains apreferred level of a reinforcing filler and a zinc alkylcarboxylateother than the necdecanoate. A few small cracks were observed on 600° F.testing.

The components listed under Example 10 in Table 3 were compounded,chilled, chipped, ground and sieved through a 200 mesh screen in theusual manner to prepare a coating powder. This powder waselectrostatically sprayed onto the various substrates, cured in a 450°F. oven for 15 minutes and tested as in Comparative Example 1. Resultsare recorded in Table 4.

EXAMPLE 11

This example discloses the performance of a coating which contains 40parts of mica reinforcing filler and the optional catalyst zincacetylacetonate. No cracks were observed on either 500 or 600° F. heatexposure. When this catalyst was used with other filler combinations,pinholes were observed (See Example 12).

The components listed under Example 11 in Table 3 were compounded,chilled, chipped, ground and sieved through a 200 mesh screen in theusual manner to prepare a coating powder. This powder waselectrostatically sprayed onto the various substrates, cured in a 450°F. oven for 15 minutes and tested as in Comparative Example 1. Resultsare recorded in Table 4.

EXAMPLE 12

This example illustrates the pinhole and bubble defects sometimesobserved when the optional catalyst zinc acetylacetonate is used as thecure catalyst.

The components listed under Example 12 in Table 3 were compounded,chilled, chipped, ground and sieved through a 200 mesh screen in theusual manner to prepare a coating powder. This powder waselectrostatically sprayed onto the various substrates, cured in a 450°F. oven for 15 minutes and tested as in Comparative Example 1. Resultsare recorded in Table 4.

TABLE 3 Compositions¹ in Parts Component Ex. 9 Ex. 10 Ex. 11 Ex. 3 Ex. 5Ex. 12 Morkote S-101 75 75 75 75 75 75 Silres 601 25 25 25 25 25 25 ZincAcac — — 0.5 — — 0.5 Zinc Stearate — 0.5 — — — — Zinc — — — 0.5 0.5 —neodecanoate C-3000 Mica 40 40 40 40 — — Orleans 325 — — — — 25 25⁽¹⁾Each coating also contained Troy 486-CFL, 2.0 phr; Benzoin, 0.8 phr.

TABLE 4 Performance Property or Performance Ex. Ex. Ex. Measure Ex. 9 1011 Ex. 3 Ex. 5 12 Gel Time (sec) 300+ 300+ 105 243 137 91 ImpactResistance (in-lb) <20 <20 60 160 20 20 Pencil Hardness B B F H F H 60°Gloss (% Reflection) 34 56 68 57 67 64 Color Change (Compared to 4.5 7.45.6 7.1 0.6 1.4 Ex. 1, white, ΔE)¹ 16 h, 500° F. Heat Age Crack Quantitynone none none none none none (per square mm)² Crack Length (mm) — — — —— — Darkening (ΔL)³ — −1.4 — 0.2 — — 16 h, 600° F. Heat Age CrackQuantity 20 10 none none 5 none (per square mm)² Crack Length (mm) .2-.5<0.2 none none .02- none .1 Darkening (ΔL)³ — −1.6 — −2.3 — — Pinholesno no no no no yes Notes: ⁽¹⁾Measured on the CIELAB scale takingred-green, blue-yellow and black-white axis into account. ⁽²⁾Cracks wereevaluated using a light microscope at 50X. ⁽³⁾Measured on the CIELABscale where black is 0 and white is 100. The unit ΔL indicates thedifference in darkness between an untested glass slide and a heat-agedone.

DISCUSSION OF THE EXAMPLES

The Effect of Resin on Color Stability, Table 5 Translucent coatings forlight-emitting devices should suffer little color change on prolongedheat exposure. Most of the coatings described herein, such as Ex. 3.,were formulated to maximize the silicone content of the binder.Comparative Example 2 is included to show the impact on color stabilityof including an organic curing agent.

TABLE 5 The Effect of Silicone Content on Color Stability Test Ex. 3 C.Ex. 2 Silicone Fraction in Binder 97 87 Color Change on 16 h, 500° F.0.2 −3.6 Exposure (ΔL)¹ Color Change on 16 h, 600° F. −2.3 −6.8 Exposure(ΔL)¹ Notes: ⁽¹⁾Positive values indicate lightening. Negative valuesindicate darkening.

The Effect of Filler on Color An attribute of any ideal coating, andespecially of translucent coatings and coatings for light-emittingdevices, is that obligatory components be colorless. The binder and anynecessary reinforcing fillers should not affect coating colors. Inseveral examples, mica was used as the reinforcing filler. At any levelemployed it was found to darken and brown the coating. This darkening ismeasurable even in Example 1, with 10 parts of mica, and becomes morenoticeable as the mica level is increase through Examples 2 and 3 andComparative Example 3. Note that a range of colors were measured at themica level of 40, suggesting that the ΔE of 6.5 for Comparative Example3 is within expected variation.

Micas of many degrees of whiteness are of course available, but it canbe advantageous to use fillers with less inherent tendency to add color,such as wollastonite and glass fiber.

TABLE 6 The Effect of Filler on Color CE Ex Ex CE Ex Ex Ex CE CE Ex ExEx Ex Component 4 1 2 2 3 9 10 3 5 5 6 7 8 Nyad 325 — — — — — — — — 25 —— — — Orleans 325 — — — — — — — — — 25 — — — Wollastonite Orleans 1Wollastonite — — — — — — — — — — 25 10 — C-3000 Mica — 10 25 40 40 40 4060 — — — — — Glass Fiber — — — — — — — — — — — — 25 Color Difference —  2.8   4.3   5.5   7.1   7.4   4.5   6.5   1.4   0.6   1.4   0.9   0.6relative to Unfilled Comp. Ex. 4 (ΔE)¹

The Effect of Filler on Smoothness. Table 7 An important attribute ofany coating, and especially of translucent coatings and coatings forlight-emitting devices, is that the coating be smooth. A measure thatcan be used to characterize smoothness is gloss. Comparative example 4shows the typical 60° gloss measure provided by a smooth, transparentcoating over aluminum, 104. As mica is added through the series Ex. 1,2, 3, and Comparative Example (CE) 3, smoothness decreases as reflectedin the dropping gloss values of 86, 68, 57, and 19. This furtherillustrates the difficulties encountered when more than about 50 partsof filler are used. Comparative Example 5 and Examples 5, 6, and 8, showthat wollastonites and glass fiber give similar loss of smoothness.

TABLE 7 The Effect of Filler on Smoothness as Seen in 60° Gloss CE Ex ExEx Ex Ex CE CE Ex Ex Ex Ex Component 4 1 2 3 9 10 3 5 5 6 7 8 Nyad 325 —— — — — — — 25 — — — — Orleans 325 — — — — — — — — 25 — — — WollastoniteOrleans 1 — — — — — — — — — 25 10 — Wollastonite C-3000 Mica — 10 25 4040 40 60 — — — — — Glass Fiber — — — — — — — — — — — 25 60° Gloss 104 8668 57 34 56 19 64 67 69 85 81

Effects of Filler Level on Crack Resistance, (See Table 2) Even smallamounts of reinforcing filler improve the resistance of these coatingsto cracking when exposed to heat, as can be seen by comparison of thegross cracking of un-reinforced Comparative Example 4 with themuch-reduced cracking of the 10 phr mica coating, Example 1 and the 10phr Wollastonite coating, Example 7. As the filler level is raised, asin the mica series CE 4, Ex. 1, 2, 3, CE 3, cracking diminishes anddisappears. This trend is repeated in the Wollastonite series CE 4, Ex.7, 6, and in comparison of other wollastonite and glass examples, CE 5and Ex. 5 and 8. to the unfilled CE 4.

Note that for many applications such as incandescent light bulbs,surface temperatures can vary widely between about 75° C. (167° F.) and400° C. (752° F.). A coating may be useful even though it exhibits minorcracking after 600° F. testing.

Effects of Wollastonite Aspect Ratio. Table 8 Comparative Example 5 andExamples 5 and 6 illustrate the effect of Wollastonite aspect ratio (theratio of length to width or diameter). As the ratio is doubled from 5:1to 10:1 in Comparative Example 5 and in Example 5, crack resistanceincreases dramatically. There appears to be an optimum aspect ratio orparticle size, as crack resistance falls somewhat with the largerparticles in Example 6.

TABLE 8 The Effects of Aspect Ratio Comp. Ex. 5 Ex. 5 Ex. 6 ReinforcingFiller Nyad 325 Orleans 325 Orleans 1 Aspect Ratio 5:1 10:1 20:1 16 h,600° F. Heat Aging Crack Quantity 20 5 25 (per square mm) Crack Length1-10 0.02-0.1 0.2-0.5 (mm)

Effects of Curing Agent. Table 9 Catalysts which promote cure improvethe crack resistance of these coatings in several ways. For example, thetendency of films to crack on heat exposure is less for the catalyzedfilms Ex. 10, 11 and 3 than uncatalyzed film Ex. 9.

Although zinc acetylacetonate in Ex. 11 and zinc neodecanoate in Ex. 3both improve the crack resistance of coatings filled with 40 phr mica,and have generally good appearance, this is not the case in coatingsfilled with lower levels of wollastonite. Ex. 5, containing 25 phrwollastonite and cured with zinc neodecanoate has a generally smoothappearance, while Ex. 12, cured with zinc acetylacelonate, exhibitslarge numbers of pinhole defects.

TABLE 9 Effects of Cure Catalysts on Performance and Appearance Ex. 9Ex. 10 Ex. 11 Ex. 3 Ex. 5 Ex. 12 Filler C-3000 C-3000 C-3000 C-3000Orleans Orleans Type Mica Mica Mica Mica 325 325 Wolla- Wolla- stonitestonite Filler 40 40 40 40 25 25 Quantity Curing none zinc zinc zinczinc zinc Agent stearate acac neodec neodec. acac 16 h, 600° F. Heat AgeCrack 20 10 none none 5 none Quantity (per square mm)² Crack .2-.5 <0.2none none .02-.1 none Length (mm) Pinholes no no no no no yes

Coated Light-Emitting Devices

EXAMPLE 13

The following components were combined in a plastic bag, shaken forthirty seconds to make a raw mix.

Component Parts Morkote S-101 75 Silres 601 25 Zinc Acetylacetonate 0.5Troy 486 CFL 2.0 Benzoin 0.8 Orleans 325 35 Heliogen Blue Pigment 4.0(BASF Corp.)

The raw mix was extruded and cooled between chilled rollers to formchips. To these chips was added 0.2 wt. % aluminum oxide dry flowadditive (Charles Wagner Co. Philadelphia). The chips were ground to apowder and sieved through a 200 mesh screen to form a coating powder.

Using this powder, PAR-type 85 watt flood lights manufactured by GeneralElectric were coated as follows:

(1) Clean bulbs by wiping with methylethylketone.

(2) Preheat at 400° F. for 3 minutes.

(3) Coat by electrostatic spray in a grounding jig to a coatingthickness of 0.8 to 1.0 mils.

(4) Cure 15 minutes at 450° F.

(5) Remove bulb from the oven and allow to air cool.

What is claimed is:
 1. A coating powder composition comprising, a binderresin system, between about 90 and 100 wt % of said binder resin systemcomprising silicone resin, and between about 0.05 and about 3 wt % of asilicone cure catalyst which is a zinc dialkylcarboxylate, wherein thedialkylcarboxylate moieties of said zinc dialkylcarboxylate are branchedat the carbon alpha to the carboxylate group.
 2. The compositionaccording to claim 1 wherein said zinc dialkylcarboxylate is zincneodecanoate.
 3. A light emitting device having a coating formed from acoating powder of a composition comprising a binder resin system,between about 90 and 100 wt % of said binder resin system comprisingsilicone resin, between about 10 and about 50 parts per hundred resin byweight of a filler selected from the group consisting of mica, calciummetasilicate, glass particles, and mixtures thereof, said filler havingaspect ratios between about 8 and about 40, and up to about 3 wt % of asilicone cure catalyst.
 4. The composition according to claim 3 whereinsaid coating, at a thickness of 1 mil, provides light transmittance ofat least about 50%.
 5. The composition according to claim 3 wherein saidcoating, at a thickness of 1 mil, provides light transmittance of atleast about 80%.
 6. A coating powder composition comprising, a binderresin system comprising silicone resin, between about 0.05 and about 3wt % of a silicone cure catalyst which is a zinc dialkylcarboxylate, andbetween about 10 and about 50 parts per hundred resin by weight of afiller selected from the group consisting of glass particles, mixturesthereof with mica, and mixtures thereof with calcium metasilicate, saidfiller having an aspect ratio of between about 8 and about
 40. 7. Acoating powder composition as claimed in claim 6, wherein thedialkylcarboxylate moieties of said zinc dialkylcarboxylate are branchedat the carbon alpha to the carboxylate group.
 8. A device as claimed inclaim 3, wherein in said composition said filler is present in an amountof between about 20 and about 40 parts per hundred resin by weight.
 9. Adevice as claimed in claim 3, wherein in said composition said filler iswollastonite.